Production of metal powders from their oxides



March 12, 1957 c. F. TEICHMANN 2,785,062

PRODUCTION OF METAL POWDERS FROM THEIR OXIDES Filed Sept. 13, 1952 (j ATTORNEY PRDUCTIN GF METAL PWDERS FRM THEIR GXEDES Charles F. Teichmann, Crestwood, N. Y., assigner to Texaco Development Corporation, New York, N. Y.,

a corporation of Delaware Application September 13, 1952, Serial No. 3%?,394

7 Claims. (Cl. 75-.5)

This invention relates to a novel method for preparing metals from their oxides. By this method metal powders can be prepared continuously, rapidly, and economically with average particle sizes smaller than 40 microns and even as small as lmicrons or less. lt is also possible to prepare liquid metals more rapidly and efficiently than heretofore. Among the metals which can be prepared by my process are those below chromium in the electrochemical series.

ln accordance with the principles of theV present invention there is provided a. novel method for producing a comminuted metal from a readily reducible metal oxide which comprises forming a owable mixture such as a slurry of particles of the metal oxide in a Vaporizable liquid, such as water or kerosene or an oil-water emulsion, for example, and passing the slurry into an elongated tubular heating zone wherein it is heated to a temperature sucient to evaporate substantially all of the liquid. Particles of metal oxide then are carried by the resulting vapor at high velocity in violently turbulent tlow through a succeeding zone in a long tube to disintegrate any solid particles and decrease eir size.

Reduction of the oxide to the metal is accomplished by reacting ythe oxide with a reducing gas such as hydrogen, carbon monoxide, or a hydrocarbon such as methane. The reactions are almost stoichiometric, less than 10 percent excess reducing gas generally suthcing. The reducing gas may be introduced into the long tube to react with the metal oxide while maintaining the high velocity turbulent tlow conditions to eiect disintegration or" particles iowing with the vapor, and while maintaining the temperature below the melting point of the metal, to produce as a product comminuted metal much liner than the particles of metal oxide initially passed into the heating zone. Alternatively, the nely divided metal roxide powder may be separated from the vapor and -then reduced in a separate reactor. Liquid metal is obtained when the temperat re in the reduction zone is above the melting point.

The invention wid be described in detail below with reference to the accompanying drawings wherein:

Fig. l is a schematic view of one 4type of apparatus suitable for performing my novel method by both grindand reducing the metal oxide in the same long tube; and

Fig. 2 is a schematic view of apparatus suitable for performing a modified embodiment of my novel method by grinding the metal om'de in a long tube, and then reducing it in a separate reactor.

1n performing my novel method particles of metal oxide are introduced into a mixer 11 wherein they are mixed intimately with a vaporizable liquid such as water or kerosene to form a pumpable slurry. The metal oxide particles should be small enough to be handled readily as a suspension or slurry, particles as large as 5 mm. diameter down to .074 mm. or less being satisfactory. Enough liquid should be added to produce a slurry which consists at least percent of liquid by weight. in some instances it may be desirable to mix an inert solid material such Statesv Patent C reducing gas employed in the operation.

as bentonite with the slurry, and a solid reducing material such as carbon can also be added, with or without the inert.

The slurry is transferred by a pump 13, such as a piston type mud pump, through a preheater 15 and into an elongated coiled tube 17 contained within a heater 19, such as a fuel-tired furnace. A tube 17 having an inside diameter of 1A. inch and a length of 15G to 1,000 feet can be used. lt need not necessarily be coiled for operability of the method, but a coil is advantageous for compactness and heating eiciency.

The initial section of the tube 17 constitutes the heating zone in which the liquid is heated up to its boiling point and the particles of metal oxide are also concurrently heated. Part-way through the tube 17 the boiling temperature is reached and the liquid is converted to a large volume of vapor which flows at a high velocity in an extremely turbulent manner through the tube, carrying particles of disintegrating metal oxide with it. The vapor and metal oxide particles then pass out of tube 17 into a similar coiled long reaction tube 18 having several spaced inlets for reducing gas connected to a supply conduit 21.

The reducing gas immediately starts to react with the particles of metal oxide llowing turbulently at high velocity with the vapor in tube 18 and converts them to metal as they pass through the -tube to its outlet 23. Further reduction in particle size occurs in tube 18.

The reducing reaction is suiliciently exotherrnic with most metal oxides that external heating of the reaction tube 1S usually is unnecessary to maintain high velocity vapor ow. ln fact, so much heat energy generally will be liberated that tube 18 should be cooled, as by water jets from a sprayer 24, when an economically high production rate is employed. Cooling can be dispensed with when a suticiently small throughput of metal oxide is employed, and when the reducing fluid is sufficiently dilute, but a lower production rate is then obtained.

Tubes 17 and 1S actually/.constitute two parts of a single long tube wherein grinding and reducing occur. lt is apparent that both 17 and 13 could be composed of two or more parts, each lying within its own heating furnace or cooling vessel, or they could both be loca-ted within the same enclosure.

The extremely high velocity turbulent flow maintained within the tubes 17 and 18 causes the particles of metal oxide, before reduction, and the particles of metal, after reduction, to impinge against one another and distintegrate to powder of greatly decreased size compared to the particles of ordde originally in the slurry.

The vapor and metal powder are discharged from the tube 1S through outlet 23 and flow to a separator 25 such as a conventional cyclone separator wherein the vapor and metal particles'are separated from one another, the metal dropping out of suspension and being discharged as a substantially dry powder through the outlet Z7, and the vapor (including any excess reducing gas and gaseous products of the reaction) leaving at the top through an outlet 29.

For economy the separated hot vapor is passed by a conduit 31 to slurry preheater 15V. Any uncondensedvapor then passes to a scrubber 32 wherein all but the excess reducing gas is removed, after which the excess reducing gas passes by a conduit 33 into the supplyconduit 2l.

The type of scrubber 32 depends uponthe type of When the reducing gas is hydrogen, it is only necessary to condense water vapor. When the reducing fluid is carbon monoxide it is only necessary to absorb carbon dioxide in a caustic solution, or the like. When the reducing fluid is a hydrocarbon, such as methane,V provision must be made both `for condensing water vapor and forv'absorbing carbon dioxide.

. 3` Further economy Ycan be realized -by recycling condensed water to the mixer 11, if desired. Any nelydivided metal carried over with the separated vapor can be iltered or scrubbed out if such recovery is economically justied. Any unconverted metal oxide leaving the separator can be segregated andrecycled tothe mixerl. I 'Y ln carrying out the method described above it is advantageous for the slurry entering the tube 17 to have Ya linear velocity at least between 1/z and l0 feet per second, suitably about l foot per second. Eicient Vgrinding of solid material in the tubes 17 and 18 is obtained when the vapor velocity therein is between 100 and 3,000 feet per second,with velocities above 200 feet per second being especially desirable. Higher Yvelocities may be used, and pressures up lto 500 pounds per square Y inch gauge or higher can be used.

The reduction temperatures vary for the diiferent metal oxides, typical examples being set forth below. With f Y 2,785,062; f

oxide at about 310 C.; lead monoxide at about 185 C.; Y

and cadmium oxide at aboutV 280 C. Iron oxide can be reduced by hydrogen'Y at 500K-600 C.; nickel oxide Vat about 300 C.; cobalt oxide at 50G-600 C. (reduction starting at about 165 C.); tin oxide at 700-800 C.; vmanganese monoxide at `about l,200 C.; but at a considerably lower temperature at high pressures, e. g., 200 C. at 150 atm. Cobalt oxide can be reduced with carbon monoxide at about 600 C. Lead monoxide can be reduced with methane atabout 750 C. The reaction temperature actually employed should in every case be high enough to assure the production of suiiicient steam or other vapor for grinding. The top temperature should be below the melting point of the metal. when metal powder is wanted, since molten metal would be produced above the melting point.

Using the production of finely-divided copper metal from copper oxide particles as an example, the Vprinciples o the invention may be applied by first making up a water slurry consisting of about 50 percent by weight of copper oxide particles ranging between'.l77 and 4.776 mm. in size. This slurry is pumped at a rate of 1,000 pounds per hour into a 1A. inch I. D. tube 17 which is 200 feet long and thence into tube 1S. Tube 17 is heated to a temperature of about 220 C., and a pressure of about 95 pounds per'square inch gauge is maintained at outlet 23. Meanwhile, gaseous hydrogen is pumped into the tube 1S, which is 400'feet long, at a rate of 2,500 cubic feet per hour to react exothermically with the hot fine particles of copper oxide and produce an extremely finely-divided copper powder product. Since the reaction is quite exothermic it is important to control the temperature in the tube 1S, as by spraying water over the tube from the sprayer 24 to prevent damage to the apparatus.

In the embodiment of the invention illustrated in Fig. 2, the metal oxide is introduced into the system and initially ground in the same manner as described in connection with Fig. l. However, before the reduction takes place the finely ground metal oxide is separated from the steam or other vapor, after which the reducing gas picks up and fluidizes the powdered copper oxide to carry out the reducing reaction.

More in detail, the metal oxide and liquid are combined to form a slurry in a mixer 41 and the slurry is then passed in high velocity turbulent flow through a preheater 43 and a grinding coil 45 to disintegrate the copper oxide particles, and then into the separator 47. Vapor passes by a conduit 49 to the preheater 43. Hot copperoxide is passed out through a bottom exit 50 and is carried by a reducing gas, such as gaseous hydrogen from a supply conduit 49, into a reactor 51 wherein jthe reduction takes place. The temperature of the reactants should be at least C. to initiate the reaction. The initial section of reactor 51 can be heated mildly to assure such a temperature. Since the'reaction is exothermic the temperature 4should be controlled in the latter part of the reactor 51, as by spraying water thereon from a water spray device 55.

it is advantageous for the reactor S1 to be a long coiled tube like the tube 18 of Fig. l, andfor the Vreducing gasto ow in such volume and at such a high rate that a violently turbulent `ilow occurs whichrfurther .decreasesV the size of the particles passing through the tube. VHowever, when no further size reduction is requiredwthe` reactor 51 can be a simple chamber.

The reduced metal and accompanying gases pass from reactor 5i by a conduit 57 to a separator 59 from which the metal powder product is discharged through a bottorn exit 61, and the .gases are discharged at the top through a conduit 63. Y

The heat of the off-gases in conduit 63 may be utilized by passing them through a hydrogen preheater 65. From there Lany uncondensed gases llow to a scrubber 67 wherein all but the excess reducing gas is removed. Then the excess reducing gas ows back into the supply conduit 49. e

While it is not known for certain Vjust what is the mechanism of the grinding lthat takes place in tubes 17 and 1S, 45 and 51, it is believed that the extremely turbulent ow at high Velocity produces innumerable collisions of the solid particles with one another thus causing their VdisintegrationV to an extremely line state such that the average diameter of particles is of the order of l-S microns. There also may be some particle size reduction due to the rapid expansion and contraction eects on the particles and the violent transfer of energy to the particles within the heating zone when liquid is vaporized from the particles.

My novel method is particularly advantageous because it will produce the linest metal powder continuously, rapidly, and economically without requiring an independent grinding step. It is also of particular value because water vapor will not accumulate on thefparticle surfaceV to inhibit the reaction, as in static reduction methods.

The use of a slurry from which liquid is vaporized to carry the `solid particlesin a iiuidized condition through the .system is another important advantage over prior procedures involving the uidizing of solids. prior procedures'the solidV particles must be-suspended directly in an expensively compressed gas by complicated apparatus, and a'higher ratio of gas to'solid is required than in the present invention.

Obviously many modifications and variations of the invention, as hereinbefore set forth, maybe made without departing from the spirit andV scope thereof, and therefore only such limitations should be imposed as are indicated inthe appended claims. Y

Iclaim: Y Y Y 1. A method for producing comminuted metal from Imetal oxide which comprises forming a slurry of particles of said metal `oxide in a vaporizable liquid; passing said slurry in-to a heating zone; heating said slurry to a temperature Vsuflicient to evaporate substantially'all of said liquid to vapor; passing said particles of metal oxide with said vapor through a long tube in turbulent iiow and at a high velocity suiiicient to effect disintegration of particles of said metal oxide flowing with said vapor; discharging said vapor and metal oxide particles from said tube; separating said metal oxide particles from said vapor; and passing said metal oxide particles into a reactor while concurrently passing a reducing gas through said reactor in intimate relation with said metal oxide particles and while maintaining the temperature below the melting point of said metal, to reduce said metal In such oxide particles to metal powder much finer than the particles of metal oxide in said slurry.

2. A method in accordance with claim 1 also comprising the step of passing said separated vapor in heat exchange relation with said slurry before said slurry enters said heating zone.

3. A method in accordance with claim 1 wherein said reactor is a second long tube, and wherein said metal oxide and said reducing gas ow together in high velocity turbulent ow -through said second tube to decrease still further the size of metal particles.

4. A method in accordance W-ith claim l also comprising the steps of separating reduced metal particles from the gas leaving said reactor; and recycling excess reducing gas into said reactor.

5. A method in accordance with claim 4 also cornprising the step of passing said separated gas in heat exchange relation with the reducing gas entering said reactor.

6. A method in accordance with claim 1 also comprising the steps of separating reduced particles from the gas leaving said reactor; scrubbing said gas to remove therefrom ingredients other than unreacted reducing gas; and recycling the reducing gas so recovered into said reactor.

7. A method for producing comminuted metal from an oxide thereof which comprises forming a owable mixture of relatively coarse particles of said oxide in a vaporizable liquid; passing said mixture into an elongated tubular heating zone; heating said mixture during passage through said tubular zone to a temperature sucient to vaporize substantially all of said liquid during passage through said zone, forming therein a dispersion of solid oxide particles in result-ing vapor; passing said dispersion through a succeeding zone of high velocity ow While subjecting the owing stream therein to turbulence and a high velocity sucient to etect disintegration of said coarse particles of oxide flowing with said vapor; discharging said vapor and said metal oxide particles from said succeeding zone; separating said metal oxide particles from said vapor; and passing said metal oxide particles into a reactor while concurrently passing a reducing gas through said reactor in intimate relation with said metal oxide particles and while maintaining the temperature below the melting point of said metal to reduce said metal oxide particles to a metal powder much liner than the particles of metal oxide in said slurry.

References Cited in the le of this patent UNITED STATES PATENTS 2,481,226 Krebs Sept. 6, 1949 2,515,542 Yellot July 18, 1950 2,538,201 Kalbach et al I an. 16, 1951 2,552,603 Tanner May 15, 1951 2,567,959 Munday Sept. 18, 1951 2,586,818 Harms Feb. 26, 1952 2,669,509 Sellers Feb. 16, 1954 2,677,608 McKay et al. May 4, 1954 OTHER REFERENCES The Canadian Mining and Metallurgical Bulletin for April 1949, pp. 181, 182. 

1. A METHOD FOR PRODUCING COMMINUTED METAL FROM METAL OXIDE WHICH COMPRISES FORMING A SLURRY OF PARTICLES OF SAID METAL OXIDE IN A VAPORIZABLE LIQUID; PASSING SAID SLURRY INTO A HEATING ZONE; HEATING SAID SLURRY TO A TEMPERATURE SUFFICIENT TO EVAPORATED SUBSTANTIALLY ALL OF SAID LIQUID TO VAPOR; PASSING SAID PARTICLES OF METAL OXIDE WITH SAID VAPOR THROUGH A LONG TUBE IN TURBULENT FLOW AND AT A HIGH VELOCITY SUFFICIENT TO EFFECT DISINTEGRATION OF PARTICLES OF SAID METAL OXIDE FLOWING WITH SAID VAPORF DISCHARGING SAID VAPOR AND METAL OXIDE PARTICLES FROM SAID TUBE; SEPARATING SAID METAL OXIDE PARTICLES FROM SAID VAPOR; AND PASSING SAID METAL OXIDE PARTICLES INTO A REACTOR WHILE CONCURRENTLY PASSING A REDUCING GAS THROUGH SAID REACTOR IN INTIMATE RELATION WWITH SAID METAL OXIDE PARTICLES AND WHILE MAINTAINING THE TEMPERATURE BELOW THE MELTING POINT OF SAID METAL, TO REDUCEE SAID METAL OXIDE PARTICLES TO METAL POWDER MUCH FINER THAN THE PARTICLES OF METAL OXIDE IN SAID SLURRY. 